Cermaic tile grout is starting to crumble

Hi, i just got tile installed and the grout is starting to crumble on the grout line. Some say that the grout is to thick and fat. Is there anything that i can do to stop it from crumbling? Any products, cauking or can i regrout it myself? Please help!!!! Thanks so much in advance

Crumbling grout is generally a sign of movement in the substrate. Not all floors are suitable for a tile installation. Who verified suitability prior to making the installation? Re-grouting probably isn't the answer.